1. Field of the Invention
The present invention relates to an improved electrode structural body and a rechargeable battery provided with said electrode structural body. More particularly, the present invention relates an improved electrode structural body having a specific electrode material layer and which is suitable for use, particularly in rechargeable batteries such as rechargeable lithium series batteries and rechargeable zinc series batteries (these rechargeable batteries will be hereinafter referred to simply as rechargeable battery) and a rechargeable battery provided with said electrode structural body and which is always highly safe and stably exhibits excellent battery performances while preventing the generation of growth of a dendrite of lithium or zinc upon the repetition of the charging and discharging cycle, and which has a prolonged cycle life (a prolonged charging and discharging cycle life).
The present invention also relates a process for the production of said electrode structure and a process for the production of said rechargeable battery.
2. Related Background Art
In recent years, increasing levels of atmospheric CO2 has been predicted to cause increase in the earth""s temperature, due to the green house effect.
In the case of the steam-power generation, increasing amounts of a fossil fuel represented by coal or petroleum are being consumed for power generation in order to comply with a societal demand for increased power supply. Along with this, the amount of exhaust Ones from the steam-power generation plants has also been continuously increased while accordingly increases the amount of greenhouse gases such as carbon dioxide gas in the air. This results in an earth-warming phenomenon. In order to prevent the earth-warming phenomenon from further developing, prohibitions on newly established steam-power generation plants have been implemented in some countries.
Under these circumstances, use of load leveling has been proposed in order to effectively utilize the power generator, where rechargeable batteries are installed in locations and a surplus power unused in the night, a so-called dump power, is stored in these rechargeable batteries, the power thus stored is supplied in the daytime when the power demand is increased, whereby the power generator is leveled in terms of the load therefor.
In recent years, electric vehicles which do not exhaust any air polluting substances such as COx, NOx, hydrocarbons, and the like and are of low impact to the environment have been developed. For such electric vehicle, there is an increased demand for developing a high performance rechargeable battery with a high energy density which can be effectively used therein.
On the other hand, there is also an increased demand for developing a miniature, lightweight, high performance rechargeable battery usable as a power source for potable instruments such as small personal computers, word processors, camcorders, and cellular phones.
As such rechargeable battery, there has proposed various rocking chair type lithium ion batteries in which a carbonous material such as graphite capable of intercalating lithium ion at intercalation sites of its six-membered network plane provided by carbon atoms in the battery reaction upon charging is used as an -anode material and a lithium intercalation compound capable of deintercalating said lithium ion from the intercalation in the battery reaction upon charging is used as a cathode material. Some of these lithium ion batteries hive been practically used. However, in any of these lithium ion batteries, the theoretical amount of lithium, which can be intercalated by the anodes is only an amount of ⅙ per carbon atom. Therefore, using this battery design, it is impossible to attain a desirable rechargeable battery having a high energy density comparable to that of a primary lithium battery in which metallic lithium is used as the anode active material.
Further, in such lithium ion battery, when the amount of lithium intercalated by the anode is made greater than the theoretical amount or charging is conducted under condition of high electric current density, there will an unavoidable problem such that lithium is deposited in a dendritic state (that is, in the form of a dendrite) on the anode comprising the carbonous material during the charging operation. This will result in causing internal-shorts between the anode and the cathode upon repeating the charging and discharging cycle, wherein there cannot attain a sufficient charging and discharging cycle life. in addition, it is difficult to operate charging with such high electric current density in the case of a rechargeable battery in which a conventional aqueous series electrolyte solution is used.
Now, rechargeable lithium batteries in which a metallic lithium is used as the anode have been proposed and they have attracted public attention in a viewpoint that they exhibit a high energy density. However, such rechargeable battery is not practically usable one because its charging and discharging cycle life is extremely short. A main reason for this has been generally considered as will be described in the following. The metallic lithium as the anode reacts with impurities such as water or an organic solvent contained in an electrolyte solution to form an insulating film or/and the metallic lithium as the anode has an irregular surface with portions. to which electric field is converged, and these factors lead to generating a dendrite of lithium upon repeating the charging and discharging cycle, resulting in internal-shorts between the anode and cathode. As a result, the charging and discharging cycle life of the rechargeable battery is extremely shortened.
When the lithium dendrite is formed to make the anode and cathode such that they are internally shorted with the cathode, the energy possessed by the battery is rapidly consumed at the internally shorted portion. This creates problems in that the battery is heated or the solvent of the electrolyte is decomposed by virtue of heat to generate gas, resulting in an increase in the inner pressure of the battery. These problems result in damaging the rechargeable battery or/and shortening the lifetime of the battery.
Use of a lithium alloy such as lithium-aluminum alloy as the anode for a rechargeable lithium battery has been proposed as a way to suppress the reactivity of the lithium with water or an organic solvent contained in the electrolyte solution to prevent lithium dendrite formation. However, this is not practical for the following reasons. The lithium alloy is difficult to fabricate into a spiral form and therefore, it Is difficult to produce a spiral-wound cylindrical rechargeable battery. Accordingly, it is difficult to attain a desirable charging and discharging cycle life for a rechargeable battery obtained, and the rechargeable battery, it is difficult attain a: desirable energy density similar to that of a primary battery in which a metallic lithium is used as the anode.
Japanese Unexamined Patent Publications Nos. 64239/1996, 62464/1991, 12768/1990, 113366/1987, 15761/1987, 93866/1987, and 78434/1979 disclose various metals, i.e., Al, Cd, In, Sn, Sb, PC and Bi as the metal capable of forming an alloy with lithium in a rechargeable battery when the battery is subjected to charging, and rechargeable batteries in which these metals, alloys of these metals, or alloys of these metals with lithium are used as the anodes.
However, these documents do not detail about the configurations of the anodes. And any of the rechargeable batteries disclosed in these documents is problematic in that when any of the alloy materials is fabricated into a plate-like form, such as a foil form which is generally adopted as an electrode of a rechargeable battery and it is used as an anode of a rechargeable battery in which lithium is used as an active material, the surface area of a portion contributing to the battery reaction in the electrode material layer is relatively small and therefore, the charging and discharging cycle is difficult to be conducted with a large electric current. Further, for a rechargeable battery in which any of the foregoing alloy materials is used the anode, there are such problems as will be described in the following. The anode is expanded with respect to the volume because of alloying with lithium upon charging and shrunk upon discharging, where the anode suffers from repetitive variations in the volume. Because of this, the anode has a tendency that it is eventually distorted and cracked. And when the charging and discharging cycle is repeated over a long period of time, in the worst case, the anode is converted into a pulverized state to have an increased impedance, resulting in shortening the charging and discharging cycle life. Hence, none of the rechargeable batteries disclosed in the above Japanese documents has been put to practical use.
Japanese Unexamined Patent: Publication No. 202675/1985 proposes an anode for a rechargeable battery in which a non-aqueous electrolyte is used, said anode being an anode having an improved porosity rate obtained by providing a composition composed of powder of a given metal or alloy, a binder and a filler soluble in a solvent, compression-molding said composition into a body and immersing said body in a solvent to dissolve the filler contained therein. This document describes that a rechargeable lithium battery in which said anode is used provides an improved charge-and-discharge capacity at a relatively high current density of more than 2 mA/cm2. However, this Japanese document is silent about the charging and discharging cycle life of the battery.
EXTENDED ABSTRACTS WED-02 (pp. 69-72) ON 8TH INTERNATIONAL MEETING ON LITHIUM BATTERIES (hereinafter referred to as document WED-02) describes that by electrochemically depositing a Sn material or a Sn-alloy material on a copper wire of 0.07 mm; in diameter as a collector, an electrode having a deposited layer comprising a grained tin material with a small particle size of 200 to 400 nm can be formed, and a battery in which the electrode having such deposited layer with a thin thickness of about 3 xcexcm and a counter electrode comprising lithium metal are used, has an improved charging and discharging cycle life. Document WED-02 further describes that in the evaluations in which charging was conducted up to 1.7 Li/Sn with a current density of 0.25 mA/cm2, an electrode having a layer comprising a fine-grained tin material of 200 to 400 nm in particle size deposited on a collector comprising a copper wire of 0.07 mm in diameter prepared in accordance with the foregoing manner, an electrode comprising an alloy of Sn0.91Ag0.09 and an electrode comprising an alloy of Sn0.72Sb0.28 were greater than an electrodes having a layer comprising a coarse-grained tin material of 2000 to 4000 nm in particle size obtained by depositing a Sn-alloy material on a collector comprising a copper wire of 1.0 mm, in diameter in the same manner as described in the above, in terms of the charging and discharging cycle life, respectively by about 4 times, about 9 times, and about 11 times. However, in document WED-02, the evaluated results are those obtained by using the lithium metal as the counter electrode as above described. Document WED-02 does not describes anything about results evaluated in practical battery configurations. And the foregoing electrode having the fine-grained thin layer of 200 to 400 nm in particle size is one prepared by electrochemically depositing the Sn material or Sn-alloy material on the copper wire of 0.07 mm in diameter. Therefore this electrode is not usable in a practical rechargeable battery. Further, the foregoing electrode having the coarse-grained tin layer of 2000 to 4000 nm in particle size is one prepared by depositing the Sn-alloy material on the copper wire of 1.0 mm in diameter. It is understood that this electrode is apparently inferior in terms of the charging and discharging cycle life.
Japanese Unexamined Patent Publications Nos. 190171/1993, 47381/1993, 114057/1988 and 13264/1988 describe rechargeable batteries in which various lithium alloys are used as the anodes and in which the generation of a dendrite is prevented so as to have an improvement in the charging efficiency and the charging and discharging cycle life.
Similarly, Japanese Unexamined Patent Publication No. 234585/1993 describes a rechargeable battery having an anode comprising a lithium metal whose surface being uniformly adhered with a powdery metal difficult to form an intermetallic compound with lithium in which the generation of a dendrite is prevented so as to have an improvement in the charging efficiency and the charging and discharging cycle life.
However, the anode in any of the rechargeable batteries described in these publications is insufficient particularly in terms of the battery lifetime.
Journal of Applied Electrochemistry, 22, 620-627 (1992) discloses a rechargeable lithium battery in which the anode is constituted by an aluminum foil having a surface applied with etching treatment. However, the rechargeable lithium battery disclosed in this document is problematic in that when the charging and discharging cycle is repeated under standard use conditions for the ordinary rechargeable battery, the aluminum foil is repeatedly expanded and shrunk, eventually cracking, resulting in a reduction in the current collecting performance, wherein the growth of a dendrite is liable to occur. Hence, it is difficult for the rechargeable lithium battery described in this document to have a practically usable charging and discharging cycle life.
The above situation in the conventional rechargeable lithium batteries is similar in the conventional rechargeable zinc series batteries including nickel-zinc batteries and rechargeable zinc-oxygen (or zinc-air) batteries. That is, in any of these zinc series batteries, problems are liable to occur in that upon repeating the charging and discharging cycle, a dendrite of zinc as the anode constituent is often generated and grown to penetrate the separator, resulting in causing internal-shorts between the zinc anode and the cathode, where the charging and discharging cycle life is shortened.
Accordingly, there is an increased demand for an improved, highly reliable rechargeable battery which possesses a high energy, density (or charge energy density) and a prolonged charging and discharging cycle life.
The term xe2x80x9crechargeable batteryxe2x80x9d herein and hereunder is meant to include a rechargeable lithium battery in which intercalation-deintercalation reaction in accordance with the oxidation-reduction reaction of lithium ion due to charge and discharge is used, and a rechargeable zinc series rechargeable battery in which zinc is used as the anode.
The rechargeable lithium battery herein is meant to include a rechargeable lithium battery in which a carbonous material is used as the anode. The rechargeable zinc series battery herein is meant to include a rechargeable nickel-zinc battery, a rechargeable zinc-oxygen battery and a rechargeable bromine-zinc battery.
The present invention has been accomplished in view of the above-described nm situations in the prior art.
An object of the present invention is to provide an improved electrode structural body in which an anode active material comprising lithium or zinc is used and which is desirably usable in a rechargeable battery and a rechargeable battery provided with said electrode structural body and which has a high energy density and a prolonged charging and discharging cycle life.
Another object of the present invention is to provide an improved electrode structural body having an electrode material layer comprising 35% by weight or more of a grained host matrix material comprising host matrix material particles of 0.5 to 60 xcexcm in average particle size formed on a surface or opposite surfaces of a plate-like shaped collector.
A further object of the present invention is to provide a rechargeable battery comprising at least an anode, a cathode and an electrolyte and in which charging and discharging are operated utilizing oxidation-reduction. reaction of an anode active material, wherein said anode comprises an electrode structural body having an electrode material layer comprising 35% by weight or more of a grained host matrix material comprising host matrix material particles of 0.5 to 60 xcexcm in average particle size formed on a surface or opposite surfaces of a plate-like shaped collector.
The grained host matrix material comprising host matrix material particles such specific average particle size in the present invention will be hereinafter referred to simply as xe2x80x9cgrained host matrix materialxe2x80x9d or xe2x80x9chost matrix material particlesxe2x80x9d for simplification purposes.